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31.
针对多孔结构内气体表观渗透率受稀薄效应的影响而显著高于其固有渗透率的现象,从孔隙尺度流线的几何拓扑特性出发,提出了利用固有渗透率、孔隙率、弯曲度和收缩-扩张因子来表示多孔结构的有效孔隙尺寸的方法,并将该有效孔隙尺寸与经典的稀薄气体管道流动模型相结合,理论推导出一种新的多孔结构稀薄气体渗透率模型。利用该模型,可以在孔隙几何结构和物性状态已知的条件下对气体的表观渗透率进行预测。随后,通过高精度的直接模拟Monte Carlo方法(DSMC)对提出模型的准确性进行验证。通过对Knudsen数在0.01~10范围、孔隙率在0.17~0.90范围、不同气体工质以及多种有序性孔隙形式下的气体流动过程进行数值模拟表明,所提出的理论模型与模拟数据的平均偏差小于10%。 相似文献
32.
金属多孔网幕具有比表面积大、物理稳定性好等诸多优点,广泛应用于推进剂在轨气液分离及相变传热等领域。泡破压力是衡量其相分离性能的关键参数,可根据多孔介质的有效泡破孔径确定。然而多孔网幕的孔隙结构极其复杂,泡破孔径计算仍未有通用且高效的方法。建立了一种基于三维孔隙结构的多孔网幕泡破压力的通用型解析模型。该模型仅依赖于多孔网幕的几何结构参数,无须实验即可有效预测多孔网幕的泡破压力。模型预测结果与本文实验及文献实验中不同网幕规格、低温及常温工质数据吻合良好,平均误差仅为8%,表明该解析模型具有普适性和准确性,可为基于多孔网幕的液体获取装置的设计与性能预测提供参考。 相似文献
33.
Space reactors with fast neutron energy spectrums are preferred for their compactness and high fission power density, but require a high fissile inventory. The operation life estimates of these reactors are important to mission planning. This paper examines a number of fuel depletion and neutronics code packages for determining the operation lives of two space reactors with hard fast neutron energy spectra. These are: the lithium-cooled, Sectored, Compact Reactor (SCoRe-S11), and the submersion subcritical safe space (S^4) reactor, cooled with a He–Xe binary gas mixture (40 g/mol). This work investigated the code packages of Monteburns 2.0, MCNPX 2.6C and TRITON and validated their prediction with fuel depletion data for a PWR fuel bundle, with satisfactory results. The operation life predictions of the two space reactors using these code packages are compared with those calculated using a simplified method that couples MCNP5 to a burnup analysis model using the Simulink® platform. This method considers only the 10 most probable low-Z and high-Z elements of the fission yield peaks plus 149Sm, and neglects the depletion of fission products due to capture and radioactive decay. The simplified method requires significantly shorter running time and its predictions of the operation lives for the two space reactors are within 0.29–12.5% of those obtained using Monteburns 2.0 and MCNPX 2.6C code packages. This method, however, is not recommended for operation life predictions for space or commercial reactors with thermal neutron spectrums. 相似文献
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The drilling operation occupies an important position in the aircraft assembly workload, and it accounts for a large proportion of the assembly cost. Previous reports show that drilling quality affects aircraft safety factor such as the probability of fatigue failure accidents. This paper proposes an automatic machining system for curved surface drilling. In this scheme, the self-adaption normal direction is realized by using the secondary positioning strategy (primary positioning and precise positioning). An elastic structure and the key positions smooth processing are applied to enhance the positioning guidance. The active variable stiffness mechanism satisfies the different requirements for system stiffness during the positioning stage and the drilling stage. Expansion sleeve locking and state switching of drilling assistance pneumatic cylinder lead to changes in the actuator's DOF and external forces, thereby achieving active control of the stiffness. Vibration-assisted machining technology is introduced to improve drilling quality. Compared with conventional drilling, the results show that this drilling system produces thin and slender chips, smaller burrs, and better internal surface quality. 相似文献
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基于现役某型号运载火箭一级伺服回路的控制方案和原理,提出一种在发射场一级发动机挂齿后进行自动归零的方法.经发射场试验实际验证:一级发动机喷管在实施自动归零措施后可快速回零且不发生偏离,自动归零方案可行有效. 相似文献
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The effects of coverage area on fatigue crack growth (FCG) properties of 6061-T6 aluminum alloy subject to multiple laser peening (LP) impacts were investigated. Residual stress, micro-structure and fatigue striation pattern on fracture cross-sections were analyzed. Compressive residual stresses and dense dislocation arrangements can be found in the superficial layer after LP. LP coverage area has a direct influence on FCG properties as verified by different size of shell ridges and fatigue striation spacing on fracture cross-sections. Meanwhile, FCG rate decreases with the increase of compressive residual stresses distribution perpendicular to the crack growth direction in the initial FCG stage. 相似文献